In a manufacturing process of a semiconductor device or an FPD (flat panel display), a plasma is often used in processes, e.g., etching, deposition, oxidation, sputtering and the like, in order to make a processing gas react efficiently at a relatively low temperature. Conventionally, a capacitively coupled plasma processing apparatus capable of generating a plasma of a large diameter is mainly used for a single-wafer plasma processing apparatus.
Generally, in the capacitively coupled plasma processing apparatus, an upper and a lower electrode are disposed in parallel with each other in an evacuative processing chamber, and a substrate to be processed (e.g., a semiconductor wafer, a glass substrate or the like) is mounted on the lower electrode. By applying a high frequency power (an RF power) to both electrodes, electrons accelerated by a high frequency electric field formed between the electrodes, secondary electrons emitted from the electrodes, or heated electrons collide with molecules of a processing gas to generate ions. Accordingly, a plasma of the processing gas is generated, and a required microprocessing, e.g., etching, is performed on a substrate surface by radicals or ions in the plasma.
In the etching process, there is widely used a lower dual frequency application mode in which a first RF power preferably having a relatively high frequency wave (generally greater than or equal to about 40 MHz) for plasma generation (RF discharge) and a second RF power preferably having a relatively low frequency wave (generally lower than or equal to about 13.56 MHz) for ion attraction to the substrate (bias) are simultaneously applied to a lower electrode.
Meanwhile, with increasing demands for miniaturization and high integration of devices in the semiconductor processing technique, a high efficiency, high density and low bias plasma processing is required in the capacitively coupled plasma processing apparatus. To do so, the high frequency wave for plasma generation tends to be set as high as possible. Meanwhile, along with the tendency to increase the chip size and the diameter of the substrate, the plasma is required to be of a larger diameter and, therefore, a chamber (processing vessel) is scaled up accordingly.
Here, the problem is that it is difficult to get uniform plasma density within the processing housing (especially in a radial direction) of the chamber. That is, if RF frequency for discharge increases, standing wave is formed within the chamber (the wave effect) or more RF wave is concentrated around the central part of the surface of an electrode (the skin effect). Roughly speaking, therefore, the density of plasma becomes nonuniform in the form of the profile with the maximum at the central part on the substrate and with the minimum at the edge part. If plasma density is not uniform on the substrate, the plasma processing may not be uniform and the manufacturing yield of devices goes down.
To that end, various electrode structures have been developed. For example, in a plasma processing apparatus described in Japanese Patent Laid-open Application No. 2004-363552 and corresponding US Patent Application Publication No. 2005-0276928, uniformity in a plasma density distribution is improved by inserting a dielectric member in a main surface of an electrode facing a processing space so that an impedance to a high frequency power emitted from the main surface of the electrode to the processing space increases at a central portion of the electrode and decreases at an edge portion of the electrode.
The technique for inserting a dielectric member in a main surface of an electrode is disadvantageous in that the impedance distribution on the main surface of the electrode is fixed by a profile and a material of the dielectric member. Accordingly, a process region where the uniformity of the plasma density distribution can be controlled is small. Further, it is not possible to flexibly cope with various processes or changes of processing conditions. In addition, a recent tendency of an increasing variety of processing gases and a widening processing pressure range employed in the plasma processing makes it harder to satisfy uniformity, and thus it is required to develop a control scheme to arbitrarily tailor the plasma distribution.
Moreover, in the so-called lower electrode dual frequency application technique, the first RF power of higher frequency and the second RF power of lower frequency exhibit different characteristics of field intensity distribution on the main surface of the lower electrode. Conventionally, however, the first and second RF powers are superimposedly applied to the same lower electrode through a same power feed line and, therefore, it is difficult to simultaneously optimize plasma density distribution characteristics (which depend on the field intensity distribution characteristics of the first RF power) and the self-bias voltage distribution characteristics (which depend on the field intensity distribution characteristics of the second RF power) on a target substrate mounted on the lower electrode. For instance, there is a trade-off problem, i.e., improvement of plasma density uniformity resulting in deterioration of anisotropic etching uniformity.